Impact of space charges on the saturation curves of ionization chambers

We apply a perturbation method to quantify the impact of space charge accumulation on the output current of ionization chambers. We then obtain the formulae of the saturation curves delivered by these detectors under the form of series for which we calculate the first coefficients. The spatial variations of the primary charge density are taken into account in the calculations. For uniform ionization rates, we demonstrate that the amplitude of the space charge perturbations depends only on the values of the electronic and ionic Langevin factors of the filling fluid. We show that the influence of space charges can be neglected when the Langevin factor, λ, is small. These results were confirmed using numerical resolutions of the charge propagation equations. Finally, we evaluate the voltage that delimits the transition between the recombination regime and the saturation plateau when the space charges are taken into account.